1. Field of the Invention
This invention relates to flat panel display devices and, more particularly, to processes for creating fiber spacer structures which provide support against the atmospheric pressure on the flat panel display without impairing the resolution of the image.
2. State of the Art
In flat panel displays of the field emission type, an evacuated cavity is maintained between the cathode electron-emitting surface and its corresponding anode display face. Since there is a relatively high voltage differential between the cathode electron-emitting surface and the display screen, it is important to prevent catastrophic electrical breakdown between them. At the same time, the narrow spacing between the plates is necessary for structural thinness and to obtain high image resolution. Spacer structures incorporated between the display face and the baseplate perform these functions.
In order to be effective, spacer structures must possess certain characteristics. They must have sufficient nonconductivity to prevent catastrophic electrical breakdown between the cathode array and the anode. This is necessary because of both the relatively close inter-electrode spacing (which may be on the order of 200 xcexcm) and relatively high inter-electrode voltage differential (which may be on the order of 300 or more volts).
Further, the supports must be strong enough to prevent the flat panel display from collapsing under atmospheric pressure. Stability under electron bombardment is also important, since electrons will be generated at each of the pixels. The spacers must also withstand xe2x80x9cbake-outxe2x80x9d temperatures of around 400xc2x0 C. used in forming the high vacuum between the faceplate and baseplate of the display.
For optimum screen resolution, the spacer structures must be almost perfectly aligned to array topography. They must be of sufficiently small cross-sectional area so as to be invisible during display operation. Hence, cylindrical spacers must have diameters no greater than about 50 microns. A single cylindrical lead oxide silicate glass column, having a diameter of 25 microns and a height of 200 microns, will have a buckle load of about 2.67xc3x9710xe2x88x922 newtons. Buckle loads, of course, will decrease as height is increased with no corresponding increase in diameter.
It is also of note that a cylindrical spacer having a diameter d will have a buckle load that is only about 18% greater than that of a spacer of square cross-section and a diagonal d, although the cylindrical spacer has a cross-sectional area about 57% greater than the spacer of square cross-section.
Known methods for spacer fabrication using screen-printing, stencil printing, or glass balls do not provide a spacer having a sufficiently high aspect ratio. The spacers formed by these methods either cannot support the high voltages or interfere with the display image. Other methods which employ the etching of deposited materials suffer from slow throughput (i.e., time length of fabrication), slow etch rates, and etch mask degradation. The use of lithographically defined photoactive organic compound results in the formation of spacers which are incompatible with the high vacuum conditions and elevated temperatures characteristic in the manufacture of field emission displays (FED).
Accordingly, there is a need for a high aspect ratio spacer structure for use in a FED and an efficient method of manufacturing a FED with such a spacer.
A process for fabricating high-aspect ratio support structures is provided. The process comprises creating a rectangular fiber bundle of glass strands, wherein contiguous groups of glass strands form a pattern. The pattern can be of a variety of shapes, including a cross T, I-beam, rail, or bracket. The fiber bundle is sliced into xe2x80x9ctilesxe2x80x9d and adhered to an electrode plate of an evacuated display.
The fiber bundle is comprised of groups of selectively etchable glass strands, which may or may not be coated with a resistive material. The glass strands are preferably square in cross-section and are, therefore, stackable. The etchable and nonetchable strands are stacked in a desired pattern in the bundle; the bundle is drawn to thereby increase its length and decrease its diameter, while maintaining its shape and pattern. Several bundles are then stacked and drawn into a fiber boule. The fiber boule is sliced into rectangular tiles. Adhesive is deposited on the electrode plate of the vacuum display to hold the tiles in the desired locations, and the tiles disposed about the display plate. Some of the glass fibers are then selectively removed, thereby creating support structures.
In an alternative embodiment of the present invention, a process for forming spacers useful in large area displays is disclosed. The process comprises forming rectangular bundles comprising fiber strands held together with a binder, slicing the bundles into rectangular slices, adhering the slices onto an electrode plate of the display, and removing the binder. The ends of the glass fibers may be polished, and the binder near the ends of the glass fibers etched back. The binder is then removed, thereby creating spacers.
One advantage of this method of stacking fibers in a pattern and forming boules therefrom is that collimated spacers are made in an accurate, repeatable pattern, not easily attainable when other shapes, such as round fibers, are utilized. This reduces the cost of manufacturing the panel, as well as the weight of the panel. The use of such spacers enables the sintering of thin panel glass substrates, while holding off the forces due to atmospheric pressure. This technique will also result in high aspect ratio spacers, so higher resolution can be attained without having the output image adversely affected by the presence of spacers. This technique also increases the chances that the fiber strand is orderly and regularly distributed in the glass boule. The evenly collimated distribution is maintained throughout the spacer forming process, thereby improving the yield in the percentage of fibers adhering onto the adhesive dots.